1. Field Of the Invention
The present invention relates to a circuit device and a method of manufacturing the circuit device, and particularly to a thin type circuit device and a manufacturing method of the circuit device which eliminates the need of a support substrate.
2. Description of the Related Art
Conventionally, the circuit device that is set on the electronic equipment is demanded to be smaller, thinner, and lighter, so that it can be employed in the portable telephones or the portable computers.
For example, the semiconductor devices as the circuit device are typically of the package type which is conventionally sealed by normal transfer molding. This semiconductor device is mounted on a printed circuit board PS as shown in FIG. 29.
This package type semiconductor device has a semiconductor chip 2 covered with a resin layer 3, and a lead terminal 4 for outside connection derived from a side portion of this resin layer 3.
However, this package type semiconductor device 1 with the lead terminal 4 extending out of the side face of the resin layer 3 was too large in whole size to satisfy the requirements of smaller, thinner and lighter constitution.
Therefore, the companies have developed various structures to realize the smaller, thinner and lighter semiconductor devices, and recently, what is called a CSP (Chip Size Package) has been developed, including a wafer scale CSP as large as the chip size or a CSP slightly larger than the chip size.
FIG. 30 shows a CSP 6 that uses a glass epoxy substrate 5 as the support substrate and is slightly larger than the chip size. Herein, a transistor chip T is mounted on the glass epoxy substrate 5.
A first electrode 7, a second electrode 8, and a die pad 9 are formed on the surface of this glass epoxy substrate 5, and a first back electrode 10 and a second back electrode 11 are formed on a back surface thereof. And the first electrode 7 and the first back electrode 10, as well as the second electrode 8 and the second back electrode 11 are electrically connected via a through hole TH. Also, the bare transistor chip T is fixed on the die pad 9, in which an emitter electrode of the transistor is connected with the first electrode 7 via a bonding wire 12, and a base electrode of the transistor is connected with the second electrode 8 via the bonding wire 12. Further, a resin layer 13 is provided on the glass epoxy substrate 5 to cover the transistor chip T.
The CSP 6 employs the glass epoxy substrate 5, but has a simple structure extending from the chip T to the back electrodes 10, 11 for outside connection, unlike the wafer scale CSP, with a merit of low manufacturing costs.
The CSP 6 is mounted on the printed circuit board PS, as shown in FIG. 29. The printed circuit board PS is provided with the electrodes and interconnects making up an electrical circuit, to which the CSP 6, the package type semiconductor device 1, a chip resistor CR and a chip condenser CC are electrically connected and fixed.
A circuit constituted by this printed circuit board is installed on various sets.
Referring now to FIGS. 31 and 32, a manufacturing method of this CSP will be described below. In FIG. 32, a flowchart entitled as a glass epoxy/flexible substrate in the center is referred to.
First of all, a glass epoxy substrate 5 as the base substance (support substrate) is prepared. The Cu foils 20, 21 are bonded via an insulating adhesive on the both sides (see FIG. 31A).
Subsequently, Cu foil 20, 21 corresponding to the first electrode 7, the second electrode 8, the die pad 9, the first back electrode 10, the second back electrode 11, are covered with an anti-etching resist 22, and then the Cu foils 20, 21 are patterned. The patterning may be performed separately on the front and back sides (see FIG. 31B).
Subsequently, a pore for the through hole TH is formed through the glass epoxy substrate, using a drill or laser. Then, this pore is plated to make the through hole TH. Via this through hole TH, the first electrode 7 and the first back electrode 10, as well as the second electrode 8 and the second back electrode 11 are electrically connected (see FIG. 31C).
Further, though omitted in the drawings, the first electrode 7 and the second electrode 8 which become the bonding posts are plated with Au, and the die pad 9 which becomes a die bonding post is plated with Au to make die bonding of the transistor chip T.
Lastly, the emitter electrode of the transistor chip T and the first electrode 7, as well as the base electrode of the transistor chip T and the second electrode 8 are connected via the bonding wire 12, and covered with the resin layer 13 (see FIG. 31D).
As required, the individual electrical elements are divided by dicing. In FIG. 31, the glass epoxy substrate 5 is only provided with one transistor chip T, but practically, a number of transistor chips T may be provided like a matrix. Therefore, the electrical elements are separated individually by a dicing apparatus lastly.
With the above manufacturing method, the CSP type electrical element employing the support substrate 5 can be completed. This manufacturing method is also applicable to the case of employing a flexible sheet as the support substrate.
On the other hand, a manufacturing method employing a ceramic substrate is shown in a flowchart to the left of FIG. 32. After the ceramic substrate to make the support substrate is prepared, a through hole is formed. Then the front and back electrodes are printed using a conductive paste, and sintered. Thereafter, the steps are performed in the same way as the manufacturing method of FIG. 31 up to covering the resin layer in the previous manufacturing method. However, the ceramic substrate has the problem that it is very fragile, and easily breaks off, unlike the flexible sheet or glass epoxy substrate, and can not be molded using a mold. Therefore, the sealing resin is potted, cured, and then polished to make a flat surface. Lastly, the electrical elements are separated using a dicing apparatus.
Further there is a demand for a lithium ion cell of small size and large capacity with the spread of portable terminals. A protection circuit substrate for battery management of charging or discharging this lithium ion cell must be small in size and withstand the short-circuit with the load, owing to the needs for the lighter portable terminal. Such protection circuit substrate is accommodated within a container of the lithium ion cell, and required to be smaller and thinner. For this purpose, the COB (Chip on Board) technology making use of a lot of chip components was freely employed to meet the demands for the smaller and thinner constitution. On the other hand, since a switching element is connected in series with the lithium ion cell, the on resistance of this switching element needs to be suppressed to a quite small value, which is an essential factor to lengthen the service time or stand-by time in the portable telephone.
In order to implement this small on resistance (RDS (on)), the chips with increased cell density were developed by using minute processing in manufacturing the chips.
More specifically, a planar structure in which the channels are formed on the surface of semiconductor substrate had a cell density of 7,400,000 cells/square inches, and an on resistance of 27 mxcexa9. However, in the first generation of trench structure in which channels are formed on the side face of trench, the cell density was greatly increased to 25,000,000 cells/square inches, and the on resistance was decreased to 17 mxcexa9. Further, in the second generation of trench structure, the cell density was 72,000,000 cells/square inches, and the on resistance was decreased to 12 mxcexa9. However, there are some limitations on the minute structure to further decrease the on resistance.
FIG. 34 is a cross-sectional view of a power MOSFET that is mounted on the protection circuit substrate. There is a blanking frame made of copper, and a power MOSFET bare chip 3 is fixed by a preform material 2 made of solder or silver paste on a header 1 of this frame. On a lower surface of the power MOSFET bare chip 3, a drain electrode is formed by deposition of gold (not shown). A gate electrode and a source electrode are formed by deposition of aluminum on an upper surface thereof. A drain terminal 5 of the frame is connected to the header 1, and directly connected to the drain electrode. The gate electrode and the source electrode are electrically connected to a gate terminal and a source terminal 7, using a gold bonding fine wire 4. Accordingly, to decrease the on resistance, it is important that the resistance of the frame material, the preform material, the material of bonding fine wire 4, and the electrode material of source electrode on the upper face of chip has also effects on the on resistance of the power MOSFET.
FIGS. 35 and 36 are plan views for explaining the prior art in which the bonding fine wire is devised to decrease the on resistance.
FIG. 35 is a view illustrating four bonding fine wire 4 for connecting the source electrode with the source terminal 7 to improve the current capacity. FIG. 36 is a view illustrating the bonding fine wires 4 for connecting the source electrode with the source terminal 7, two short wires and two long wires, to improve the current capacity, and further to decrease the resistance of the source electrode by broadening the bonding region on the source electrode.
FIG. 33 is a table showing the differences of the on resistance depending on the mounting structure of the conventional power MOSFET. Sample A and sample B is concerned with the molding structure with the conventional SOP8 outer shape, sample A corresponding to a structure of FIG. 35 and sample B corresponding to that of FIG. 36. Instead of the four bonding fine wires, in a combination of two short fine wires and two long fine wires, the on resistance is decreased by 1.33 xcexa9m from 13.43 mxcexa9 to 12.10 mxcexa9, as shown in the table.
In FIG. 30, the transistor chip T, the connecting means 7 to 12, and the resin layer 13 are required components for the electrical connection with the outside and the protection of the transistor. However, these components were so insufficient that it was difficult to fabricate an electrical circuit element that can realize the smaller, thinner and lighter constitution.
The glass epoxy substrate 5 that becomes the support substrate is unnecessary in essence, as previously described. However, in the manufacturing method, because the electrodes are pasted together, the glass epoxy substrate 5 is employed as the support substrate and is not unnecessary.
Therefore, this glass epoxy substrate 5 is used, which increases the costs. Further, because the glass epoxy substrate 5 is thick, the circuit element is thickened, imposing some limitations on the smaller, thinner and lighter constitution.
Further, a though hole formation process for connecting the electrodes on the both sides is requisite in the glass epoxy substrate or ceramic substrate, leading to the problem that the manufacturing process is lengthened.
Further, the bonding wire 12 is connected by drawing a loop, which also impedes the realization of the thinner constitution.
Further, at present, the portable terminals have been demanded to be smaller in size and lighter in weight, and have a longer life of service time of the self-contained battery. Among others, there is the problem that any effective solving means to implement the low on resistance has not yet been found by doing away with the power MOSFET mounting structure and the assembling method.
A manufacturing method of assembling the power MOSFET with one sheet of frame has been conventionally established, but the leading out of the electrode on the upper face of the semiconductor chip is made by wire bonding. Also, there is the problem that any solving means has not been found to improve the on resistance of the power MOSFET in consideration of leading out the source electrode that is a current passing electrode on the upper face of semiconductor chip with the most significant effect.
Further, the above method of assembling the conventional power MOSFET with one sheet of frame employs the bonding wire. Hence, there is the problem that the molding resin is made thicker by a loop height of the bonding wire, which impedes the thinner structure.
The present invention has been achieved in the light of the above-mentioned problems, and intends to obtain a thin and reliable semiconductor device.
Firstly the invention provides a circuit device comprising a plurality of conductive paths that are electrically isolated, a circuit element having a front electrode fixed on a desired conductive path, a metal connecting plate for connecting a back electrode of said circuit element with a desired conductive path, and an insulating resin for covering said circuit element and integrally supporting said conductive paths. Hence, only minimum amount of components can be employed to solve the conventional problems.
Secondly, the invention provides a circuit device comprising a plurality of conductive paths that are electrically isolated by a trench, a circuit element having a front electrode fixed on a desired conductive path, a metal connecting plate for connecting a back electrode of said circuit element with a desired conductive path, and an insulating resin for covering said circuit element and being filled in said trench between said conductive paths to integrally support said conductive paths. Hence, a plurality of conductive paths are integrally supported by the insulating resin being filled in the trench to solve the conventional problems.
Thirdly, the invention provides a circuit device comprising a plurality of conductive paths that are electrically isolated by a trench, a circuit element having a front electrode fixed on a desired conductive path, a metal connecting plate for connecting a back electrode of said circuit element with a desired conductive path, and an insulating resin for covering said circuit elements and being filled in said trench between said conductive paths to integrally support said conductive paths, with only the back face of said conductive paths exposed. Hence, the through hole for electrical connection with the back face of the conductive paths can be eliminated to solve the conventional problems.
Fourthly, the invention provides a method of manufacturing the circuit devices comprising the steps of forming the conductive paths in such a way as to prepare a conductive foil, and to form a trench shallower than the thickness of said conductive foil in said conductive foil except for at least an area that becomes a conductive path, fixing a front electrode of a circuit element on a desired conductive path, connecting a back electrode of said circuit element with a desired conductive path via a metal connecting plate, molding an insulating resin to cover said circuit element and be filled in said trench, and removing said conductive foil in a thick portion where said trench is not provided. Hence, the conductive foil to make the conductive paths is a start material, in which the conductive foil has a support function till the insulating resin is molded, and the insulating resin has the support function after molding. Consequently, the support substrate can be dispensed with to solve the conventional problems.
Fifthly, the invention provides a method of manufacturing the circuit devices comprising the steps of forming the conductive paths in such a way as to prepare a conductive foil, and to form a trench shallower than the thickness of said conductive foil in said conductive foil except for at least an area which becomes a conductive path, fixing each front electrode of a plurality of circuit elements on a desired conductive path, connecting each back electrode of said circuit elements with a desired conductive path via a metal connecting plate, molding an insulating resin to cover said plurality of circuit elements and be filled in said trench, removing said conductive foil in a thick portion where said trench is not provided, and severing said insulating resin to separate the circuit devices individually. Hence, a number of circuit devices can be mass-produced to solve the conventional problems.
Sixthly, there is provided a MOSFET mounting structure comprising a plurality of conductive paths that are electrically isolated, a MOSFET chip having a gate electrode and a source electrode fixed on the desired conductive paths, a metal connecting plate for connecting a drain electrode of said MOSFET chip with a desired conductive path, and an insulating resin for covering said MOSFET chip and integrally supporting said conductive paths. Hence, the bonding wire is eliminated and the source electrode is fixed directly to the conductive path, thereby implementing the low on resistance.
Seventhly, there is provided a method of manufacturing the circuit devices comprising the steps of forming the conductive paths in such a way as to prepare a conductive foil, and to form a trench shallower than the thickness of said conductive foil in said conductive foil except for at least an area that becomes a conductive path, fixing a gate electrode and a source electrode of a MOSFET chip on the desired conductive paths, connecting a drain electrode of said MOSFET chip with a desired conductive path via a metal connecting plate, molding an insulating resin to cover said MOSFET chip and be filled in said trench, and removing said conductive foil in a thick portion where said trench is not provided. Hence, the manufacturing method of mass production can be provided in the flip chip method in which the bonding step is eliminated.